Liquid crystal display device

ABSTRACT

Provided is a liquid crystal display device in which a source line is divided in a screen and the screen is driven in a horizontally divided state. A divided position ( 40 ) between a source line ( 30   u ) in an upper display region and a source line ( 30   d ) in a lower display region is arranged at an intersecting part between a source line ( 30 ) and a gate line ( 32 ). A part of the source line ( 30 ), which overlaps with a gate line ( 32   a ) on which the divided position  40  is present, has a planar shape additionally including an expanded part ( 46 ) (protruding portion) having the same area as a removed part of the source line ( 30 ) at the divided position ( 40 ), as compared to a part of the source line ( 30 ), which overlaps with a gate line ( 32   b ) on which the divided position ( 40 ) is absent.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese applicationJP2012-031221 filed on Feb. 16, 2012, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device, andmore particularly, to a technology of horizontally dividing a screeninto a plurality of display regions and vertically scanning thosedisplay regions in a parallel manner.

2. Description of the Related Art

Liquid crystal display devices are used in products such as a flat paneltelevision set, a personal computer, a tablet terminal, and asmartphone. Particularly in the application of a large-sized panelrepresented by the flat panel television set, there are demands forincrease in number of pixels such as 4K resolution (4K2K) and higherframe rate driving such as dual speed and quad speed, for image displayin higher resolution, three-dimensional display, and improvement inmoving image quality. Those demands require shorter data writing time tobe allocated for each horizontal scanning line during vertical scanningof a screen, and hence there may arise a problem in that data writing toa pixel becomes insufficient when a general driving method is employed.As a countermeasure for this problem, there is known a division drivingmethod of dividing the screen into a plurality of display regions, andwriting data into the plurality of display regions in a parallel manner.For example, Japanese Patent Application Laid-open Nos. Hei 09-258163and Hei 10-48595 each describe a liquid crystal display device employingthe division driving method of horizontally dividing the screen into twoupper and lower display regions and driving the two display regions.

For example, in the division driving method of horizontally dividing thescreen into two upper and lower display regions A_(U) and A_(D) anddriving the two display regions A_(U) and A_(D), the vertical scanningof sequentially selecting gate lines (scanning wiring lines) of theupper half display region A_(U) and the vertical scanning ofsequentially selecting gate lines of the lower half display region A_(D)are performed in a parallel manner. In order to write video signals topixel rows selected in the respective display regions A_(U) and A_(D) ina parallel manner, at the boundary between the regions A_(U) and A_(D),source lines (video wiring lines) are each divided into a source linearranged in the region A_(U) and a source line arranged in the regionA_(D).

SUMMARY OF THE INVENTION

Dividing the source line in the screen affects operation of a pixel rowin the vicinity of the divided position, and there has been a problem inthat a difference in display state is generated between the pixel rowand other pixel rows. One of the influences caused by the dividingrelates to rubbing processing of an alignment film. FIG. 4 is aschematic partial plan view of a conventional liquid crystal displaydevice, in which a screen is driven in a horizontally divided state, inthe vicinity of the divided position of the source line. A TFT substrateincludes thin film transistors (TFTs) 1, source lines 2, and gate lines3, and further an alignment film stacked thereon. The alignment film hasan uneven surface due to steps of the source lines 2 formed therebelow.The unevenness of the region in the vicinity of the source line 2 isdifferent between the vicinity of a divided position 4 of the sourceline 2 and in a region of the source line 2 in the vicinity of aposition other than the divided position 4. As a result, a region inwhich the alignment film cannot be sufficiently rubbed and the liquidcrystal alignment cannot be controlled may expand on a pixel effectiveregion (aperture region) side more in the region in the vicinity of thedivided position 4 than in the region in the vicinity of the positionother than the divided position 4. For example, as illustrated in FIG.4, a region 5 in which alignment control is impossible, which isgenerated in the vicinity of the divided position 4, may expand into thepixel effective region in which a pixel electrode 6 is arranged. Whenliquid crystal is controlled to obtain a non-transmissive state throughvoltage application, liquid crystal in the region in which alignmentcontrol is impossible remains in a transmissive state. Thus, there hasbeen a problem in that a pixel having an effective region adjacent tothe divided position 4 and other pixels have a difference in brightnesswith respect to the same pixel data.

The present invention has been made to solve the above-mentionedproblems, and provides a liquid crystal display device in which a screenis driven in a horizontally divided state, which is capable ofpreventing generation of a difference in display state between a pixeladjacent to a divided position of a source line and other pixels,thereby improving image quality.

According to an exemplary embodiment of the present invention, there isprovided a liquid crystal display device, including: a pair ofsubstrates arranged opposed to each other while sandwiching liquidcrystal therebetween; scanning wiring lines extended on one of the pairof substrates along rows of pixels arranged in matrix, respectively, forapplying a selection voltage which enables writing of a pixel signal tothe pixel rows; and video wiring lines extended on the one of the pairof substrates along columns of the pixels, respectively, for supplyingthe pixel signal to corresponding one of the pixel rows, to which theselection signal is applied, the liquid crystal display device employinga division driving method of performing vertical scanning for each of aplurality of display regions obtained by horizontally dividing a screen,in which each of the video wiring lines is divided for each of theplurality of display regions, in which the each of the video wiringlines has a divided position arranged at a part intersecting withcorresponding one of the scanning wiring lines, and in which the each ofthe video wiring lines has a part which overlaps with the correspondingone of the scanning wiring lines, on which the divided position ispresent, the part having a planar shape additionally including anexpanded part having the same area as a removed part of the each of thevideo wiring lines at the divided position, as compared to a part of theeach of the video wiring lines, which overlaps with corresponding one ofthe scanning wiring lines on which the divided position is absent.

According to another exemplary embodiment of the present invention,there is provided a liquid crystal display device, including: a pair ofsubstrates arranged opposed to each other while sandwiching liquidcrystal therebetween; scanning wiring lines extended on one of the pairof substrates along rows of pixels arranged in matrix, respectively, forapplying a selection voltage which enables writing of a pixel signal tothe pixel rows; video wiring lines extended on the one of the pair ofsubstrates along columns of the pixels, respectively, for supplying thepixel signal to corresponding one of the pixel rows, to which theselection signal is applied, the liquid crystal display device employinga division driving method of performing vertical scanning for each of aplurality of display regions obtained by horizontally dividing a screen;and a light blocking film for covering a pixel separation regionprovided between the pixels adjacent to each other in a horizontaldirection, in which each of the video wiring lines extends in a verticaldirection through the pixel separation region, and is divided for eachof the plurality of display regions by providing a divided position inthe pixel separation region, and in which, in corresponding one of thepixels adjacent to the divided position, the light blocking film has aplanar shape including a convex portion projecting in the horizontaldirection in vicinity of the divided position, and in the pixels notadjacent to the divided position as well, the light blocking film hasthe planar shape so that the respective pixels have a uniform pixelaperture ratio.

In the exemplary embodiment of the present invention, the convex portionof the light blocking film covers a region in which alignment control ofthe liquid crystal is impossible, the region being generated in thevicinity of the divided position.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic view illustrating a configuration of a liquidcrystal display device according to embodiments of the presentinvention;

FIG. 2 is a schematic partial plan view of the liquid crystal displaydevice according to a first embodiment of the present invention in thevicinity of a divided position of a source line;

FIG. 3 is a schematic partial plan view of a liquid crystal displaydevice according to a second embodiment of the present invention in thevicinity of a divided position of a source line; and

FIG. 4 is a schematic partial plan view of a conventional liquid crystaldisplay device, in which a screen is driven in a horizontally dividedstate, in the vicinity of a divided position of a source line.

DETAILED DESCRIPTION OF THE INVENTION

In the following, modes for carrying out the present invention(hereinafter referred to as embodiments) are described with reference tothe drawings.

First Embodiment

FIG. 1 is a schematic view illustrating a configuration of a liquidcrystal display device 10 according to a first embodiment of the presentinvention. The liquid crystal display device 10 includes a liquidcrystal panel 20, scanning line driving circuits 22 u and 22 d, videoline driving circuits 24 u and 24 d, a control device 26, a backlightunit (not shown), and a backlight driving circuit (not shown).

The liquid crystal display device 10 employs, for example, an in-planeswitching (IPS) method and an active matrix driving method. The liquidcrystal panel 20 includes a color filter substrate and a TFT substrate,which are arranged opposed to each other with a gap, and liquid crystalis filled in the gap therebetween.

On a surface of the TFT substrate on the liquid crystal side, there areformed TFTs, source lines, gate lines, pixel electrodes, and a commonelectrode. Specifically, the pixel electrodes and the TFTs arerespectively arranged in matrix so as to correspond to the pixelarrangement. In each pixel, the common electrode is arranged as well,which is made of a transparent electrode material similarly to the pixelelectrode. Source lines 30 are provided for respective columns of theTFTs (lines in the vertical direction), and are each connected in commonto sources of a plurality of TFTs in the corresponding column. Gatelines 32 are provided for respective rows of the TFTs (lines in thehorizontal direction), and are each connected in common to gateelectrodes of a plurality of TFTs in the corresponding row. Each of thesource lines 30 is arranged along a pixel separation region providedbetween pixel columns, and each of the gate lines 32 is arranged along apixel separation region provided between pixel rows. Further, theplurality of source lines 30 and the plurality of gate lines 32 arearranged so as to substantially intersect with each other. Each of theTFTs has a drain connected to the pixel electrode corresponding to theTFT.

On a surface of the color filter substrate on the liquid crystal side, ablack matrix and a color filter are formed. The black matrix is a lightblocking film which is formed in the pixel separation regions.

The TFT substrate and the color filter substrate each include analignment film facing the liquid crystal. The alignment film issubjected to rubbing processing.

The conduction state of the TFTs is controlled in a row unit inaccordance with a scanning pulse applied to the gate line 32. The pixelelectrode is connected to the source line 30 via the TFT in an ON state,and a signal voltage (pixel voltage) based on a pixel value is appliedfrom the source line 30. A predetermined common potential provided incommon to respective pixels is applied to the common electrode via acommon electrode wiring line. The alignment of the liquid crystal iscontrolled for each pixel by an electric field generated in accordancewith a potential difference between the pixel electrode and the commonelectrode. In this manner, the transmittance of light entering from thebacklight unit is changed so that an image is formed on a displaysurface.

The liquid crystal display device 10 employs a division driving methodof horizontally dividing a screen into two upper and lower displayregions A_(U) and A_(D), and the regions A_(U) and A_(D) are subjectedto vertical scanning in a parallel manner.

In order to carry out division driving, each of the source lines 30 isdivided into a source line 30 u arranged in the region A_(U) and asource line 30 d arranged in the region A_(D), and the source lines 30 uand 30 d are connected to the video line driving circuits 24 u and 24 d,respectively. Further, the gate line 32 in the region A_(U) is connectedto the scanning line driving circuit 22 u, and the gate line 32 in theregion A_(D) is connected to the scanning line driving circuit 22 d.

A video signal received by a tuner or an antenna (now shown), or a videosignal generated by another device such as an image reproducing deviceis input into the control device 26. Based on the input video signal,the control device 26 generates pixel data indicating a gradation valueof each pixel and outputs the generated pixel data to the video linedriving circuits 24 u and 24 d, or generates a timing signal for eachportion of the liquid crystal display device 10.

The scanning line driving circuits 22 u and 22 d select the gate lines32 in the regions A_(U) and A_(D) in order, respectively, and eachoutputs a scanning pulse to the selected gate line 32. With this, TFTsin the selected pixel row are turned ON.

The video line driving circuits 24 u and 24 d output, in synchronizationwith the selection of the gate lines 32 performed by the scanning linedriving circuits 22 u and 22 d, voltages corresponding to each pixeldata of the corresponding row to the source lines 30 u and 30 d.

FIG. 2 is a schematic partial plan view of the liquid crystal displaydevice 10 in the vicinity of a divided position of the source line 30,and schematically illustrates shapes and arrangement of a TFT 34, thesource line 30, the gate line 32, a pixel electrode 36, and a blackmatrix 38. In particular, the pixel electrode 36 is illustrated so as torepresent a pixel effective region in which liquid crystal alignment iscontrolled, and hence the pattern of the pixel electrode may bedifferent from the actual case. A divided position 40 of the source line30, which is the boundary between the source lines 30 u and 30 d, isarranged at an intersecting part between the source line 30 and the gateline 32. When the planar shape is compared between a part of the sourceline 30, which overlaps with a gate line 32 a on which the dividedposition 40 is present (overlapping part 42 a), and a part of the sourceline 30, which overlaps with a gate line 32 b on which the dividedposition 40 is absent (overlapping part 42 b), the overlapping part 42 ais different from the overlapping part 42 b not only in that theoverlapping part 42 a does not have a wiring material in the dividedposition 40, but also in that the overlapping part 42 a is additionallyprovided with an expanded part 46 for expanding the area of theoverlapping part 42 a.

The expanded part 46 has an area that is the same as the area of theeliminated wiring line of the divided position 40. With this, the amountof increase in load capacity of the gate line 32 due to the overlappingpart between the source line 30 and the gate line 32 is the same betweenthe gate line 32 a arranged at the divided position 40 and the gate line32 b not arranged at the divided position 40. Thus, the respective gatelines 32 can have the same wiring load.

As described above, the present invention solves the problem in that adifference in display state is generated between the pixel row in thevicinity of the divided position 40 of the source line 30 and otherpixel rows. Regarding this point, in this embodiment, the dividedposition 40 is arranged not on the pixel separation region locatedbetween the pixels adjacent to each other in the horizontal direction,but on the gate line 32. In this manner, it is possible to prevent therubbing failure region caused by the divided position 40 (region 5 inFIG. 4) from generating in the pixel effective region. Therefore, it ispossible to solve the above-mentioned problem in that a region in whichalignment control is impossible is generated in the pixel aperture atthe pixel row in the boundary part between the upper and lower displayregions A_(U) and A_(D), which causes a difference in display state fromother pixel rows.

On the other hand, when a part of the source line 30, which overlapswith the gate line 32, is merely removed to form the divided position40, a difference in wiring load is generated between the gate line 32 aon which the divided position 40 is present and the gate line 32 b onwhich the divided position 40 is absent. Specifically, the wiring loadof the gate line 32 a is smaller than that of the gate line 32 b. As aresult, the waveform rounding of the scanning pulse applied to the gateline 32 a is smaller than that of the gate line 32 b. Therefore, onlythe pixel row selected by the gate line 32 a differs from other pixelrows in the state and condition of the writing operation of the pixelvoltage to the pixel electrode. That is, there arises a problem in thata difference in display state is generated between the pixel rowselected by the gate line 32 a and other pixel rows.

Specifically, the pixel row selected by the gate line 32 a is faster inscanning pulse rise than other pixel rows, and hence the pixel voltageapplied to the source line 30 is written in a better manner as comparedto other rows. Therefore, even when the same pixel value is applied forthe pixel row selected by the gate line 32 a and a row adjacent thereto,there arises a problem in that the display of the row selected by thegate line 32 a becomes brighter than that of the adjacent row.

Further, the above-mentioned problem in that a difference in displaystate is generated between the row selected by the gate line 32 a andother pixel rows is caused even by the fact that a fluctuation (feedthrough) of a voltage V_(P) of the pixel electrode varies in accordancewith the waveform of the scanning pulse. This point is described in thefollowing. In frame reversing driving, the polarity of the pixel voltagewith respect to a potential V_(COM) of the common electrode is reversedfor each one frame. When the pixel voltage has a positive polarity,V_(P) increases in the selected row when the scanning pulse is applied,while when the pixel voltage has a negative polarity, V_(P) decreases.When the scanning pulse falls, V_(P) slightly decreases due to theparasitic capacitance between the drain of the TFT (or the pixelelectrode) and the gate line 32. The fluctuation of the voltage V_(P)when the scanning pulse falls is the feed through voltage, which isrepresented by ΔV.

The polarity of ΔV does not change by the frame reversion, and ΔVbecomes larger as the fall of the scanning pulse is steeper. Therefore,a center voltage V_(CNT) between V_(P) set when the pixel voltage of apositive polarity is applied and V_(P) set when the pixel voltage of anegative polarity is applied is different between the row selected bythe gate line 32 a and other rows. Specifically, the row selected by thegate line 32 a has V_(CNT) smaller than other rows. In this case, whenthere is a difference between V_(CNT) and V_(COM), a DC voltage (DCoffset) is continuously applied to the liquid crystal, which may causeimage burn-in. Therefore, V_(COM) is adjusted so that a difference withrespect to V_(CNT) is small. At this time, V_(COM) is adjusted to asuited value considering that V_(CNT) may change in accordance with thepixel voltage. However, it is difficult to suitably adjust V_(COM) whileconsidering the influence of a shift of V_(CNT) in the row correspondingto the gate line 32 a. For example, even when V_(COM) is suitablyadjusted for the row in which the divided position 40 is absent, thedifference between V_(COM) and V_(CNT) cannot be sufficiently reducedfor the row corresponding to the gate line 32 a. Therefore, for example,when an image of white display as a whole is displayed for one frameperiod, and then a halftone image is displayed, the residual imagebecomes more conspicuous in the row corresponding to the gate line 32 athan in other rows. Therefore, a difference in display state isgenerated between the row corresponding to the gate line 32 a and otherrows.

In view of this, in this embodiment, as described above, the expandedpart 46 is provided in the overlapping part 42 a so that the respectivegate lines 32 have a uniform wiring load. In this manner, theabove-mentioned problem caused because the divided position 40 isarranged on the gate line 32 is solved.

In FIG. 2, as an example of the expanded part 46, there is provided aprotruding portion protruding in the horizontal direction from each ofthe source lines 30 on both sides of the divided position 40, in otherwords, an end portion of each of the source lines 30 u and 30 d. Theexpanded part 46 may be provided to only one of the source line 30 u andthe source line 30 d.

Second Embodiment

The schematic configuration of a liquid crystal display device accordingto a second embodiment of the present invention is basically the same asthe liquid crystal display device 10 according to the first embodimentillustrated in FIG. 1. In the following description, components similarto those of the first embodiment are denoted by the same referencesymbols for simple description. This embodiment is different from thefirst embodiment in the configuration of solving the problem in that adifference in display state is generated between the pixel row in thevicinity of the divided position of the source line 30 and other pixelrows. In the following, the difference from the first embodiment isdescribed.

FIG. 3 is a schematic partial plan view of the liquid crystal displaydevice 10 in the vicinity of a divided position of the source line 30,and schematically illustrates shapes and arrangement of a TFT 34, thesource line 30, the gate line 32, a pixel electrode 36, and a blackmatrix 60. In this embodiment, a divided position 62 of the source line30, which is the boundary between the source lines 30 u and 30 d, isarranged not on the gate line 32, but on a pixel separation regionlocated between pixels adjacent to each other in the horizontaldirection. In the pixel adjacent to the divided position 62, the blackmatrix 60 has a planar shape including a convex portion 64 a projectingin the horizontal direction in the vicinity of the divided position 62.The convex portion 64 a is formed into a size and shape that can coverthe region (region 5 in FIG. 4) in which alignment control of the liquidcrystal is impossible, which is considered to be generated in thevicinity of the divided position 62 due to rubbing failure. When pixelsare present on both right and left sides of the divided position 62, theconvex portions 64 a are formed on both right and left sides.

Further, in the pixel not adjacent to the divided position 62, the blackmatrix 60 has a planar shape including a convex portion 64 b having thesame size and shape as the convex portion 64 a in the pixel adjacent tothe divided position 62. With this, the respective pixels have a uniformpixel aperture ratio.

As described above, the present invention solves the problem in that adifference in display state is generated between the pixel row in thevicinity of the divided position 62 of the source line 30 and otherpixel rows. Regarding this point, in this embodiment, the convex portion64 a covers the region in which the alignment control is impossible,which is generated in the vicinity of the divided position 62, and thusit is possible to prevent contribution to pixel brightness of lightpassing through the liquid crystal in the region in which the alignmentcontrol is impossible. Therefore, for example, in an image of blackdisplay as a whole, the pixel in the vicinity of the divided position 62can perform black display similar to that of other pixels.

Further, the convex portion 64 b is provided in the pixel not in thevicinity of the divided position 62 so that the respective pixels havethe same aperture ratio. In this manner, even when the image dataindicates brightness other than black, the pixel in the vicinity of thedivided position 62 and other pixels are displayed at the samebrightness.

Therefore, the problem in that a difference in display state isgenerated between the pixel row in the boundary part between the upperand lower display regions A_(U) and A_(D) and other pixel rows issolved.

As described above, according to the present invention, in the liquidcrystal display device in which the screen is driven in a horizontallydivided state, it is possible to prevent generation of a difference indisplay state between a pixel adjacent to the divided position of thesource line and other pixels, thereby improving image quality.

While there have been described what are at present considered to becertain embodiments of the invention, it will be understood that variousmodifications may be made thereto, and it is intended that the appendedclaims cover all such modifications as fall within the true spirit andscope of the invention.

What is claimed is:
 1. A liquid crystal display device, comprising: apair of substrates arranged opposed to each other while sandwichingliquid crystal therebetween; scanning wiring lines extended on one ofthe pair of substrates along rows of pixels arranged in matrix,respectively, for applying a selection voltage which enables writing ofa pixel signal to the pixel rows; and video wiring lines extended on theone of the pair of substrates along columns of the pixels, respectively,for supplying the pixel signal to corresponding one of the pixel rows,to which the selection signal is applied, the liquid crystal displaydevice employing a division driving method of performing verticalscanning for each of a plurality of display regions obtained byhorizontally dividing a screen, wherein: each of the video wiring linesis divided for each of the plurality of display regions; the each of thevideo wiring lines has a divided position arranged at a partintersecting with corresponding one of the scanning wiring lines; andthe each of the video wiring lines has a part which overlaps with thecorresponding one of the scanning wiring lines, on which the dividedposition is present, the part having a planar shape additionallyincluding an expanded part having the same area as a removed part of theeach of the video wiring lines at the divided position, as compared to apart of the each of the video wiring lines, which overlaps withcorresponding one of the scanning wiring lines on which the dividedposition is absent.
 2. A liquid crystal display device, comprising: apair of substrates arranged opposed to each other while sandwichingliquid crystal therebetween; scanning wiring lines extended on one ofthe pair of substrates along rows of pixels arranged in matrix,respectively, for applying a selection voltage which enables writing ofa pixel signal to the pixel rows; video wiring lines extended on the oneof the pair of substrates along columns of the pixels, respectively, forsupplying the pixel signal to corresponding one of the pixel rows, towhich the selection signal is applied, the liquid crystal display deviceemploying a division driving method of performing vertical scanning foreach of a plurality of display regions obtained by horizontally dividinga screen; and a light blocking film for covering a pixel separationregion provided between the pixels adjacent to each other in ahorizontal direction, wherein: each of the video wiring lines extends ina vertical direction through the pixel separation region, and is dividedfor each of the plurality of display regions by providing a dividedposition in the pixel separation region; and in corresponding one of thepixels adjacent to the divided position, the light blocking film has aplanar shape including a convex portion projecting in the horizontaldirection in vicinity of the divided position, and in the pixels notadjacent to the divided position as well, the light blocking film hasthe planar shape so that the respective pixels have a uniform pixelaperture ratio.
 3. The liquid crystal display device according to claim2, wherein the convex portion of the light blocking film covers a regionin which alignment control of the liquid crystal is impossible, theregion being generated in the vicinity of the divided position.